1. Field of the Invention
This invention relates to a disc-shaped information recording medium for optically recording/reproducing the information, such as an optical disc.
2. Description of the Related Art
Among optical disc systems in which a recording/reproducing track on a recording surface is scanned by a laser beam for recording/reproducing various data, there are a CLV system in which the optical disc is rotated at a constant linear velocity for recording/reproducing data, a CAV system in which the optical disc is rotated at a constant angular velocity for recording/reproducing data, and a MCAV system (modified CAV system) in which the spatial recording density is set so as to be substantially equal in both the inner and outer rims of the disc for increasing the recording density.
Heretofore, in the optical disc, either a land or a groove, formed concentrically or spirally on the recording surface, is used as a recording/reproducing track. In general, a spirally formed land is used as the recording/reproducing track TR.
There is also known a continuous servo system in which a pre-groove continuously formed along the track is used for tracking control, or a sampled servo system in which servo areas discretely formed on the track are utilized for tracking control. With the continuous servo system, the land is tracked using an optical phase difference between the land and the groove for recording/reproducing the information on or from the land, that is the recording/reproducing track.
On the recording/reproducing track, an address section is formed for recording management information for data recording/reproduction.
FIG. 2 shows the structure of an address section of an optical disc of the continuous servo system prescribed by ISO (International Organization for Standardization).
In the structure of the address section, shown in FIG. 2, VFO denotes a clock seizing signal containing a large quantity of the phase information for locking the PLL (phase locked loop) of the clock reproducing system for extracting clocks for reproducing address information, AM denotes synchronization signals for taking the timing for reproducing the address information and ID denotes the actual address information containing the error correction codes. The address section may be comprised of a plurality of sets of the above signals. In the example of FIG. 2, the above sets of signals are recorded in triplicates. The address section may be preceded by a signal SM specifying the leading end of the section.
Among known optical discs, there are a so-called ROM disc, dedicated to reproduction, a recordable RAM disc, such as a write-once disc or a magneto-optical disc, and a so-called hybrid disc having both a ROM area and a RAM area.
If, for the purpose of increasing disc capacity, the track pitch is reduced for increasing the density in the radial direction, the problem of cross-talk between tracks arises. In particular, embossed pits formed by pre-formatting seriously affect neighboring tracks.
It is therefore an object of the present invention to provide a disc-shaped information recording medium in which there is no risk of mistaken detection of an address section due to cross-talk from neighboring tracks.
It is another object of the present invention to provide a disc-shaped information recording medium in which the recording density is increased for securing a larger recording capacity.
It is still another object of the present invention to provide a disc-shaped information recording medium in which land and the groove are used as tracks for securing track continuity.
It is yet another object of the present invention to provide a disc-shaped information recording medium in which address reproduction or switching of tracking polarity in the playback system may be facilitated by the synchronization signals with different patterns being recorded on the address sections of the odd tracks and on those of the even tracks.
According to the present invention, there is provided an optical disc having a land and a groove, in which the information is recorded and/or reproduced on or from a track on the land and the groove. The optical disc has an address section having a group of address information data previously formed at a pre-set period on the track. The group of address information is arranged with an offset in the track direction in an ordered pattern.
Preferably, the land is switched to the groove or vice versa an odd number of times per turn on a track.
Preferably, the address section is arranged at switching positions from the land to the grove or vice versa.
According to the present invention, there is also provided an optical disc having a land, in which the information is recorded and/or reproduced on or from a track on a land and the groove. The land is switched to the groove or vice versa an odd number of times per turn on a track and the switching positions are aligned in the radial direction in one or more radial zones. The address section is arranged at switching positions from the land to the grove or vice versa. The address section has a first address information section and a second address information section, the first and second address information sections being at a pre-set distance from one another in the zone and offset in the radial direction.
According to the present invention, there is also provided an optical disc device for recording and/or reproducing information on or from a land and a groove on an optical disc. The optical disc device includes an optical head for recording and/or reproducing the information on or from the optical disc, means for detecting the address information formed at a pre-set period on the optical disc based on a signal from the optical head, means for applying a tracking servo to the optical head, and means for issuing a signal for switching the tracking polarity to the tracking servo means based on the signal from the address information detection means.